Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
  • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
  • B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/05—Metallic powder characterised by the size or surface area of the particles
  • B22F1/054—Nanosized particles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
  • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
  • B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
  • B22F2009/245—Reduction reaction in an Ionic Liquid [IL]

Definitions

• the present invention relates to a method for the preparation of FePt or CoPt nanoparticles in ionic liquids, which in certain embodiments constitutes a direct method for the preparation of such nanoparticles having the face-centred tetragonal (fct) crystalline form.
• the invention also provides FePt or CoPt nanoparticles obtainable by a method of the invention. Face-centred tetragonal FePt and CoPt nanoparticles, and in particular fct FePt nanoparticles, have well-known utility in a variety of applications including use in ultra-high density magnetic recording media as well as numerous biomedical applications.
• Iron- and platinum-, or cobalt- and platinum- containing nanoparticles are of commercial significance because, when in the fct crystalline form (as opposed to the face-centred cubic (fee) form), these materials have exceptionally high magnetoanisotropy.
• the magnetic anisotropy of fct FePt nanoparticles can reach 10 7 J/m 3 , one of the highest values of any known material.
• Ionic liquids have recently been found to be of utility in a number of synthetic applications. These liquids can be advantageous for use as solvents or as other types of continuous liquid phase reaction media on account of their thermal stability, inflammability and lack of volatility. There have been a small number of reports alluding to the use of ionic liquids in the context of nanoparticulate preparation. Specifically, Y Yang and H Yang (J. Am. Chem. Soc, 2005, 127, 5316- 5317) describe the synthesis of CoPt nanorods in ionic liquids. In US patent publication no. US 208/0245186 (and corresponding US patent no.
• reaction temperature 140 0 C being raised to 280 0 C
• Similar methods involving heating at even higher temperature with Pt(acac) 2 and iron pentacarbonyl as platinum and iron precursors did not result in the preparation of fct FePt, but only fee FePt (see K E Elkins et al. (Nano Letters, 2003, 3(12), 1647-1649)) where reflux in dioctyl ether at 295 0 C provided fee FePt nanoparticles; and the original S Sun et al. disclosure (infra) (where the same solvent is reported to reflux at 297 0 C).
• the report of formation of an alloy with Y-Fe 2 Oa suggests oxygen contamination.
• direct preparation of nanoparticles is meant the preparation of fct nanoparticles without the need for a post-synthetic annealing step, for example one carried out extemporaneously to the synthesis of the nanoparticles of FePt or CoPt.
• the invention provides a method of directly synthesising fct FePt or CoPt nanoparticles in an ionic liquid comprising heating in the ionic liquid a mixture comprising a substrate that is capable of providing platinum atoms and a substrate that is capable of providing iron atoms or cobalt atoms whereby to provide said fct FePt or CoPt nanoparticles.
• the invention provides a method of synthesising FePt or CoPt nanoparticles in an ionic liquid comprising heating in the ionic liquid a mixture comprising a substrate that is capable of providing platinum atoms and a substrate other than iron pentacarbonyl that is capable of providing iron atoms or a substrate that is capable of providing cobalt atoms whereby to provide said FePt or CoPt nanoparticles.
• the invention provides FePt or CoPt nanoparticles obtainable by a method according to either the first or second aspects of this invention.
• Fig. 1 shows exemplary structures of some ionic liquids.
• Figs 2A and B show typical thermogravimetric analysis plots as a function of time and temperature completed under ambient conditions (A) and inert atmosphere (B).
• Figs 3A to G shows TEMs of FePt nanoparticles made according to the present invention after increasing times and degrees of heating.
• Fig. 4A shows XRD patterns of FePt nanoparticles made according to the present invention after heating at 300 0 C for 30 minutes, 1 hour and 3 hours.
• Fig. 4B shows an expanded region of the spectrum in Fig. 4A for 3 hours' heating.
• Fig. 5 shows SQUID characterisations of FePt nanoparticles made according to the present invention.
• Figs 5A1 , 5B1 and 5C1 show ZFC-FC magnetisation curves;
• Figs 5A2, 5B2 and 5C2 show hysteresis curves obtained at 2 K.
• Fig. 6 shows a further TEM of FePt nanoparticles made according to the present invention.
• Fig. 7A shows an XRD pattern of the same FePt nanoparticles for which a TEM is depicted in Fig. 6, with Fig. 7B showing an expanded region of the XRD spectrum shown in Fig. 7A.
• Fig. 8 shows a further TEM of FePt nanoparticles made according to the present invention at four different magnifications.
• Fig. 9A shows an XRD pattern of the same FePt nanoparticles for which a TEM is depicted in Fig. 8, with Fig. 9B showing an expanded region of the XRD spectrum shown in Fig. 9A.
• Fig. 10 shows a further TEM of FePt nanoparticles made according to the present invention at four different magnifications.
• Fig. 11A shows an XRD pattern of the same FePt nanoparticles for which a TEM is depicted in Fig. 10, with Fig. 1 1 B showing an expanded region of the XRD spectrum shown in Fig. 11 A.
• Figs 12A-C show a further TEM of FePt nanoparticles made according to the present invention at three different magnifications.
• Fig. 12D shows a fast fourier transform (FFD) of the cube depicted in Fig. 12C
• Fig. 13A shows an XRD pattern of the same FePt nanoparticles for which TEMs are depicted in Figs 12A-C, with Fig. 13B showing an expanded region of the XRD spectrum shown in Fig. 13A.
• Fig. 14 shows XRD spectra, with background extracted and normalized (Fig. 14(a)- (c)), TEMs (Fig. 14(d)-( ⁇ ).
• FC-ZFC magnetization curves under 100 Oe Fig. 14(g)-(i)
• Fig. 14(J)-(O) °f FePt nanoparticles synthesised for 1 h using Na 2 Fe(CO)4/Pt(acac) 2 /[P66614J[NTf 2 ] Fig. 14(a), (d), (g) and G)).
• the present invention arises, in part, from the observation that ionic liquids may be used as a reaction medium in which to prepare fct FePt or CoPt nanoparticles and, more generally, to prepare FePt or CoPt nanoparticles from a much wider range of iron atom- providing substrates than has been hitherto recognised within the art.
• nanoparticles is an indisputably well-understood term of the art, being almost universally used across the prior art in this area of technology, including almost if not all of the prior art documents referred to in the Background section and other sections herein. Nevertheless, for the avoidance of any doubt, the size implied by the use of the term nanoparticles herein is of particles in which at least one dimension, typically diameter, is in the range of from about 1 nm to about 1000 nm (1 ⁇ m). More typically, at least one dimension, typically diameter, is in the range of from about 1 nm 100 nm, consistent with the dimensionality normally ascribed to aspects of nanoscience.
• the sizes of the nanoparticles of FePt or CoPt described herein are towards the lower end of this range, for example, in the range of from about 1 to about 20 nm. More particularly still, typical sizes of the FePt or CoPt nanoparticles described herein are in the range of from about 2.5 to 5 nm, in particular from about 3 to about 4 nm.
• FePt nanoparticles described herein are fct FePt nanoparticles have at least one dimension in the range of about 2.8 to about 4 nm.
• the FePt particles described herein will be of generally spherical geometry and all the references herein to at least one dimension may be applied to the diameter of such spherical nanoparticles.
• references to sources of iron atoms may be understood to refer to sources of cobalt atoms, whereby to refer to the preparation of CoPt nanoparticles.
• the fct FePt nanoparticles provided according to the method of the first aspect of the invention are prepared by heating an ionic liquid comprising a source of both iron and platinum atoms.
• the iron atoms may be provided by way of any convenient precursor for iron atoms as known in the art.
• the iron atoms may be provided as a consequence of decomposition of iron pentacarbonyl, the archetypical source of iron used hitherto in the preparation of FePt nanoparticles.
• any other convenient source of iron such as an iron (II) or iron (III) salt may be used. Examples include iron (III) ethoxide iron (III) acetylacetonate, iron (II) acetate and iron (II) chloride (see H L Nguyen et al., Chem, Mater, 2006, 18, 6414-6424 and references cited therein and also K E Elkins et al.
• the source of the iron particles can be the same as the source of the platinum particles, for example by way of the provision of a precursor such as FePt(CO) 4 dppmBr 2 as reported by M S Wellons et al. (infra).
• Example 13 in the patent publications is likely to have failed to produce fct FePt as a consequence of the generation of Fe-coated Pt or Pt-rich nuclei and the temperature to which the mixture was then heated, particularly given the manner in which the nuclei will have been formed, is insufficient to effect transformations from the fee to fct crystal phases.
• introduction of iron pentacarbonyl into the vessel in which it is decomposed to form iron atoms may be at a lower temperature, for example ambient temperature and the reaction then heated so as to avoid the decomposition of the iron pentacarbonyl taking place in the gaseous phase, as distinct from that having the ionic liquid as the continuous phase. If the intrinsic volatility of iron pentacarbonyl remains a problem, a method of the invention may be practised in an autoclave.
• the substrate capable of providing iron atoms is other than iron pentacarbonyl.
• the substrate that is capable of providing iron atoms constitutes a compound in which iron is present in an anionic form.
• the substrate that is capable of providing platinum atoms comprises platinum in cationic form, typically in oxidation state II.
• Particularly advantageous embodiments of the present invention arise form the recognition that the specific combination of precursors comprising cationic platinum and anionic iron allow the preparation of FePt nanoparticles in ionic liquids, which combination confers particular advantages over the prior art.
• the use of a precursor for the elemental iron in anionic form is characteristic feature of many embodiments the present invention.
• Introduction of the iron in this form offers significant advantages over iron pentacarbonyl, which has been the prevalent iron source used to date in the preparation of FePt nanoparticles.
• the anionic- containing precursor from which the FePt nanoparticles are synthesised will be present in a compound comprising Fe 2" anions.
• a particular embodiment of this is Collman's reagent, Na 2 Fe(CO) 4 , which is commercially available, for example as a dioxane complex.
• the invention is by no means so limited and the skilled person will be aware of other sources of anionic iron, in particular having an oxidation state of -II.
• Such complexes are readily available and known to the skilled person and include complexes formed between Fe 2" and ligands such as carbon monoxide, nitrous oxide and phosphines.
• a specific example of an additional compound that may be used according to these embodiments of the present invention is Fe(CO) 2 (NO) 2 .
• Other examples of anionic iron-containing substrates that may be used in accordance with the present invention will be evident to those of skill in the art. Analogously, with those embodiments of the invention directed towards CoPt nanoparticles, the use of anionic cobalt-containing precursors (particularly those of oxidation state (-1) will be well within the ability of those skilled in the art, two examples being NaCo(CO) 4 and Co(CO) 3 (NO).
• the source of atomic platinum there is no particular limitation as to the platinum-containing salt that may be employed.
• the source of platinum will be a platinum (II) salt such as Pt(acac) 2 , which is customarily used in the art.
• the relative reaction kinetics of the Fe/Co and Pt precursors should be kept in mind when selecting sources for the metals in the desired nanoparticles.
• sources of atomic platinum tend to react more quickly implying that Fe/Co precursors may advantageously be chosen to be less stable than the source of atomic platinum, e.g. (Pt(acac) 2 ).
• Pt(acac) 2 the source of atomic platinum
• a specific advantage of using anionic source of iron and a cationic source of platinum is that the anionic iron-containing compound serves as a reducing agent for the cationic platinum species in the preparation of the FePt nanoparticles.
• This has the twin advantages that greater control over the stoichiometry can be achieved since generation of the desired atoms of iron and platinum are it will be appreciated, somewhat mutually dependent. Indeed, where Fe 2" - and Pt 2+ -containing species are employed, a 1 :1 theoretical stoichiometry is achieved. Control over the stoichiometric outcome during formation of the FePt nanoparticles is beneficial since it has been reported in the literature that fct formation is observed only in.
• the FePt nanoparticles are of this stoichiometry, i.e. have a value of x between about 0.4 and about 0.6 (with respect to Fe x Pt 1-x ).
• FePt coercivity is understood to be maximised at a slight iron-rich ally composition, for example in which the x with respect to Fe x Pt 1-X is in the range of in excess of about 0.52 to about 0.60 (see S Sun et al. (infra).
• a specifically added reducing agent to reduce the cationic platinum-containing substrate (e.g. Pt(acac) 2 ) to atomic platinum since the anionic iron will serve to reduce the cationic platinum.
• a specific non-iron-containing reducing agent such as the 1 ,2-hexadecanediol or polyalcohol (for example ethylene glycol, oligoethylene glycol (e.g.
• these embodiments of the invention comprise the heating of a mixture consisting essentially of a cationic platinum-containing substrate, an anionic iron- (or cobalt-) containing substrate, an ionic liquid and, optionally, one or more surfactants that serve to stabilise, and so allow formation of, the FePt nanoparticles, and, as a further optional alternative, a silver-containing substrate (further details of which are provided below). This is because the presence of an additional reductant (in addition to the anionic iron-containing substrate) will materially affect the nature of the composition.
• an additional reductant is not excluded and may be selected from any reductant customarily used in the art, such as a diol or a polyalcohol (e.g. ethylene glycol, glycerol or 1 ,2-hexadecanediol to name but three examples).
• a diol or a polyalcohol e.g. ethylene glycol, glycerol or 1 ,2-hexadecanediol to name but three examples.
• suitable reductants typically diols or polyalcohols, will be evident to those skill in the art.
• both substrates for the desired iron and platinum atoms are cationic, for example where Fe(lll)(acac)3 and Pt(ll)(acac) 2 are employed (see K E Elkins et al. (Nano Letters, infra) a reductant will be present.
• the substrate capable of providing iron atoms is not iron pentacarbonyl.
• the iron- and platinum containing substrate(s) may be as is described above in accordance with the method according to the first aspect of the invention.
• a characteristic feature of the present invention is the formation of the desired nanoparticles in ionic liquids.
• Ionic liquids The nature of Ionic liquids is well known to those of skill in the art. Broadly speaking, an ionic liquid is salt, but one in which the ions are insufficiently well- coordinated for the compound to be other than a liquid below 150 0 C, more usually below 100 0 C, and in some embodiments even at room temperature - so-called room-temperature ionic liquids.
• ionic liquids are salts that form stable liquids at temperatures below 150 0 C or lower.
• One or more ionic liquids may be used.
• Ionic liquids with inherently low vapour pressure, allow the maintenance of constant temperature to be achieved over the course of the method of the invention, in contrast to the significant vapour pressures of the high-boiling point solvents typically used in the prior art. Such solvents inevitably cause a decrease in the temperature of a reaction vessel when the solvent condenses back in.
• Ionic liquids therefore, permit not only an advantageously elevated temperature (vis-a-vis many solvents in which FePt (and CoPt) nanoparticles have been produced in the prior art) but allow a more homogeneous temperature to be maintained throughout the reaction.
• An example of this may be understood with reference to benzyl ether, which induces a temperature drop of about 20 0 C 1 whereas all the syntheses carried out to date in accordance with the present invention have not shown any temperature drop.
• the ionic liquids of the present invention have either no, or negligible, vapour pressure.
• Organic cations that may be present in ionic liquids may include, for example, quaternary ammonium, phosphonium, heteroaromatic, imidazolium and pyrrolidinium cations.
• the counteranions present in ionic liquids are likewise not particularly limited.
• suitable anions include halide (e.g.
• the or an anion of the ionic liquid is [NTf 2 ].
• this anion with its four oxygen atoms, may be advantageous in relation to the formation of fct nanoparticles, possibly by allowing simultaneous bonding to at least two precursors.
• Other anions having similar functionality, and consequential ionic liquids, will be evident to those of skill in the art.
• Ionic liquids that may be used in include 1-butyl-3-methylimidazolium
• ionic liquids examples include P66614[NTf 2 ], [HbOt]-[NTf 2 ], [C8dabco].[NTf 2 ], Me 2 N(CHs) 6 Nn 2 ][NTf 2 ] and BMI-BF4, are depicted in Fig. 1 and these are all available commercially, e.g. from Cytec Industries, Inc., (including by contractual arrangement with the Ionic Liquids Laboratory at the Queens University of Harbor (see quill.qub.ac.uk for further details)).
• Ionic liquids can be engineered to tune their advantageous properties such as stability, vapour low pressure and solvating ability so as to be safer and more environmentally friendly than conventional volatile, organic compounds. Consequentially, and because of the possibility of recycling, use of ionic liquids can simplify synthetic reactions when it is possible to substitute such ionic liquids for conventional solvents.
• ionic liquids including tri-n-hexyl-n-tetradecylphosphonium £>/s(trifluoromethylsulfonyl)imide, (referred to herein as P66614[NTf 2 ]; and commercially available from Cytec Industries, Inc.) as a representative example of an ionic liquid, is susceptible to decomposition at temperature above 240 0 C in a normal oxygen-containing atmosphere.
• P66614[NTf 2 ] tri-n-hexyl-n-tetradecylphosphonium £>/s(trifluoromethylsulfonyl)imide
• surfactants that are not ionic liquids may be advantageous. Without wishing to be bound by theory, and summarising the various commentary in the art, these may serve to stabilise atomic iron, atomic platinum, or (nascent) FePt nanoparticles.
• Suitable surfactants which will be understood as effectively functioning as stabilising agents enabling the FePt nanoparticles to be formed within the ionic liquid, may be carboxylic acid or amines, particularly primary amines in which the carboxylic acid or amino (e.g.
• oleic acid and oleyl amine are typically included, often in the ratios described herein.
• the ratio of the surfactants to the iron- (or cobalt-) and platinum-containing precursors may be varied and this may be advantageous to undertake in certain embodiments of the invention, since adjusting these ratios can affect the size and or ability to change phase of the resultant nanoparticles (see for example the paper by M Chen et al., infra.
• the temperature at which the reaction is conducted may be varied with the routine ability of those skilled in the art so as to affect the outcome of the methods of the present invention. It will be understood, both from the detailed discussion hereinbefore, and by the skilled person, that generally higher temperatures will be expected to favour transformation of fee crystalline forms to the fct polymorph. It will also be understood that prolonged exposures to elevated temperatures, for example, for more than about 3 hours at more than about 300 C C can induce generally undesired sintering of fct (or fee) crystalline forms. Likewise, fee to fct transition tends not to take place below about 250 to 300 0 C.
• heating may be advantageously conducted at a temperature of between about 250 and about 380 0 C (for example between about 295 to about 300 0 C, or between about 300 to about 350 0 C) for between about 15 minutes to about 4 hours, for example between about 30 minutes and one or two hours.
• XRD X-Ray diffraction
• TEM transmission electron microscopy
• heating Whilst heating (time and duration) at the ultimate temperature to which the ionic solution is raised is an important consideration, it is also useful in certain embodiments to heat the initially added materials to a temperature intermediate between that at which the components submitted to the method are initially introduced, e.g. room temperature (e.g. about 20 0 C, and that to which they are ultimately heated, e.g. about 320 to about 350 0 C.
• room temperature e.g. about 20 0 C
• Imposition of such an intermediate heating regimen can have a number of advantageous effects, such as conferring a greater homogeneity of distribution of the materials dispersed or dissolved within the ionic liquid, which can manifest itself in a higher quality or more desirable outcome during later phase transition (if such is desired); by ridding the solvent of undesirable oxygen or moisture; and increasing the opportunities for complexes with the ligands (e. g. surfactants) to form.
• ligands e. g. surfactants
• the stabiliser included within the mixture that is heated to provide the FePt nanoparticles is poly(A/-vinyl-2-pyrrolidone) (PVP) as described more fully by T Iwamoto et al. (infra).
• PVP poly(A/-vinyl-2-pyrrolidone)
• no specific stabiliser is added.
• the possibility to omit a specific stabiliser which according to many embodiments of the invention and hitherto has been typically a combination of oleic acid and oleoyl amine, may be understood to be achievable for two reasons. Firstly, because of the inherent charge associated with ionic liquids, these may serve to function as dispersants as well as solvents (or other continuous liquid phases) during the preparation of FePt nanoparticles as alluded to by T Osaka ⁇ infra).
• Typical heating rates may be between about 1 to about 20 °C/min, e.g. between about 5 to about 15 c C/min.
• Another factor is the additional injection of precursors after a reaction mixture is heated, e.g. in accordance with a method of the present invention, e.g. whereby to provide fct FePt nanoparticles. Injection of material in this way can be advantageous in allowing subsequent FePt material to adopt the crystallinity of the existing nanoparticles (e.g. fct) yet provide larger nanoparticles, which may be useful for certain applications.
• one or more metals additional to iron or cobalt and platinum such as copper, zirconium, aluminium, silver and gold, may be incorporated into the desired nanoparticles.
• Silver atoms in particular, are known to enhance magnetisation and propensity to transform to fct significantly (see for example L Castaldi et al., J. Appl. Phys, 2009, 105, Art No. 93914).
• such methods of the invention comprise the heating of a mixture consisting essentially of a platinum-containing substrate, an iron- or cobalt-containing substrate, a silver-containing substrate, an ionic liquid and, optionally, one or more surfactants that serve to stabilise, and so allow formation of, the FePt or CoPt nanoparticles.
• ionic liquids can be recycled, providing a still further advantage of the present invention over traditional solvents used in the art hitherto.
• extraction of the nanoparticles produced, e.g. by magnetic extraction from the ionic liquid as opposed, for example, to a work up involving addition of an alcoholic solvent such as ethanol and washing with hexane solvent (to give on example) may permit with ease the recycling of the ionic liquid solvent and development of continuous flow systems.
• the reaction mixture was further heated up to 300 0 C for 1 to 3 h to investigate the grow mechanism.
• Nanoparticles were precipitated by ethanol addition & centrifugation. After discarding the supernatant, the precipitates were dispersed with hexane, precipitated by ethanol & collected by centrifugation. This procedure was repeated several times.
• Crystalline grain size D of FePt NPs is calculated according to Scherrer's formula.
• composition Fe x Pt 1-X value was calculated according to Vegar's law (J. W. A. Bonakdarpour, et al., J. Electrochem. Soc. 2005, 152, A61-72). Thermogravimetric analysis (TGA)
• TGA provides mass losses as a function of time. Under ambient (i.e. non-inert) conditions, ionic liquids begin to decompose rapidly at temperatures above 240 0 C after one hour at 270 0 C a sample tested lost over a quarter of its weight demonstrating that the oxygen present in air can assist in the decomposition of the ionic liquid. TGA was also carried out in an inert atmosphere. Typical plots are depicted in Fig. 2. After one hour at 320 0 C, the ionic liquid had lost only 5% of its mass and there were no significant weight losses were experienced at 270 0 C. Under inert atmospheric conditions, therefore, ionic liquids display an improved stability over traditional solvents allowing nanoparticles syntheses at higher temperatures and with limited decomposition of the liquids.
• Fig. 3 shows TEM spectra of FePt nanoparticles synthesised in P66614.[NTf 2 ] as solvent. The concentration of both iron and platinum precursors were 0.05 M respectively.
• Samples were withdrawn at [A] 200 0 C, (B) 250 0 C, (C) 300 0 C (beginning), (D) 300 0 C after 30 mins, (E) 300 0 C after one hour, (F) 300 0 C after two hours and (G) 300 0 C after three hours.
• Figs. 3A shows mainly nuclei (depicted light in colour) and small spherical nanoparticles (dark in colour).
• Fig. 3B there are clearly identifiable well- dispersed nanoparticles.
• 300 0 C Figs. 3C-G
• the nanoparticles gradually fused, with the number of fused nanoparticles cluster increasing over the time the reaction mixture is held at 300 0 C. From the time heating reaches 300 0 C until 30 minutes after heating at 300 0 C, (Figs. 3C and 3D), well-dispersed nanoparticles are still clearly visible.
• Fig. 3E shows that, after one hour at 300 C C, a small proportion of nanoparticles have fused and, after 2 and 3 hours Figs. 3F and 3G) a significant number of nanoparticles have sintered.
• Fig. 4B shows the XRD pattern of a sample withdrawn after 3 hours (2 ⁇ step size: 0.02, time/step: 1800 s).
• Table 1 XRD data of FePt NPs synthesized in P66614.[NTf 2 ] solvent. Samples were withdrawn at 300 0 C 30 min, 1 h and 3 h. 2 ⁇ is the position of the (111 ) peak, a is the lattice constant, D XRD is the crystalline grain size, x is the iron content is Fe x Pt 1-X .
• Nanoparticles were dispersed in PMMA matrix to reduce interaction that would otherwise have reduced magnetism and coercivity.
• the evolution of the magnetic properties are depicted in Fig. 5 with the left hand column (Figs 5A1 , 5B1 and 5C1 ) showing FC-ZFC curves whilst the right-hand column (Figs 5A2, 5B2 and 5C2) depicts hysteresis curves obtained at 2 K.
• Table 2 Magnetic properties of the FePt NPs synthesized in P66614.[NTf 2 ] solvent.
• T b is the blocking temperature
• H 0 is the coercivity
• M the magnetisation at saturation
• M the remanent magnetisation and MJM, their ratio
• the initial particles show a magnetic behaviour relatively independent of the reaction time, with a blocking temperature (T b ) of around 20 K.
• T b blocking temperature
• the T b is much higher with the sample after 3 hours at about 120 K.
• Figs 5A2 and B2 shows increasing of Ms from 12.2 to 13.2 emu/g & Mr from 5.5 to 5.9 emu/g as the reaction time is increased from 0.5 h to 1 h, which may indicate larger particle or better crystallinity with longer heating times.
• the decrease of Ms from 13.2 to 11.6 emu/g, Mr from 5.9 to 5.2 emu/g & Hc from 3.3 to 1.4 kOe as the reaction time is increased from 1 h to 3 h may be caused by the polycrystalline structure of those fused NPs, as intergranular exchange couple leads to reduction of magnetocrystalline anisotropy (see Rong et al., Adv.
• the reduced coercivity may also be attributed to the magnetic dipole coupling between nanocrystals.
• NPs samples were dispersed in PMMA matrix to reduce to the magnetic dipole coupling as much as possible.
• the aggregation of nanoparticles after 3 h may increase possibility the magnetic dipole coupling.
• Very likely that magnetic dipole coupling between aggregated nanocrystals is reducing the coercivity and also leads to the constricted hysteresis loops, see insert hysteresis loop in Fig. 5C2 vs. in Fig. 5A2 & 5B2 (see Lee et al., Phys Chem B, 2006, 110(23), 1 1160-11166).
• the physical size of the nanoparticles was successfully increased above 3 nm (see
• XRD XRD.
• XRD was carried out over 2 ⁇ ranger over 25 to 100 degree, with 2 ⁇ step size: 0.02, time/step: 240 s,
• B XRD was carried out over 2 ⁇ ranger over 25 to 55 degree with 2 ⁇ step size: 0.02, time/step: 1800 s.
• XRD size was increased by 14 % up to 2.5 nm.
• Ligand concentration is known to impact naparticles' growth, with the higher concentration of ligand, the more complexes formed and the slower nucleation rate (E. V. Shevchenko et a/., infra; S. Saita and S. Maenosono, infra; and V. Nandwana et a/., infra). Consequently ligand to precursor was increased by a factor 4. 8 presents the TEM results of this alteration of the protocol (P66614.[NTf 2 ] as solvent.
• Fig. 8B shows cubic, triangular, lozenge shapes with very facetted structures.
• Fig. 8C shows fringes (stable under beam). Suggests inorganic crystals. Moreover inter spacings between lattice fringes are about 0.48 nm, which are close to (1 11 ) planes of Fe 3 O 4 at 0.48405 nm, which suggested Fe 3 O 4 .
• Fig. 8D shows inter-fringes spacing 0.228 nm, 0.231 nm, 0.202 nm corresponding to fee FePt (111 ) at 0.2202 nm, (200) lattice planes at 0.1908 nm respectively.
• Formation of non-spherical shapes could be induced by high concentration of ligand.
• XRD patterns are shown in Fig. 9. XRD was carried out over 2 ⁇ ranger over 25 to 100 degree, with 2 ⁇ step size: 0.02, time/step: 240 s, (B) XRD was carried out over 2 ⁇ ranger over 25 to 55 degree with 2 ⁇ step size: 0.02, time/step: 1800 s.
• Fig. 9A shows 3 main peaks corresponding FePt (111 ), (200), (220) peaks.
• 3 small peaks labeled with arrows indicate the present of Fe 3 O 4 , they are (311 ), (400), & (440) peaks.
• the (111) peak expected to show at around 23 2 ⁇ degree is probably covered by high noise background at low 2 ⁇ range.
• the trace of iron oxide is consistent with the present of cubic or triangular Fe 3 O 4 particles suggested by HRTEM imaging. Further confirmation was carried out by EDX which also showed the composition of areas containing cubic & triangular particles is Fe rich
• Table 3 XRD data of FePt NPs synthesised by use P66614.[NTf 2 ] as solvent. Heat rate 5 °C/min. 2 ⁇ is the position of the (111 ) peak, a is the lattice constant, D XRD is the crystalline grain size, x is the iron content is FexPt1-x. Crystalline grain size D XRD of FePt samples.
• Precursor concentration is known to have a strong impact on the growth of nanoparticles and their crystallinity (E.V. Shevchenko et a/., infra; S. Saita and S. Maenosono, infra; and V. Nandwana et al., infra). Reduced precursor concentrations were used in order to reduce nucleation rate.
• Fig. 10 illustrates a TEM of a typical product of these syntheses.
• XRD patterns are shown in Fig. 11.
• XRD was carried out over 2 ⁇ ranger over 25 to 100 degree, with 2 ⁇ step size: 0.02, time/step: 240 s,
• the additional precursor injection protocol is as follows:
• a strategy known in the art to increase the size of nanoparticles is to inject, at a rate limiting new nuclei formation, more precursors as the nanoparticles are in their growth phase. This was completed after the synthetic solution reached 300 0 C for 30 min and by using the nanoparticles as nuclei while feeding their growth with additional drop-wise injection of precursors.
• TEM results are presented Fig. 12.
• Fig. 12A polydisperse in size & shape.
• Fig. 12B spherical & cubic NPs. Size of spherical NPs 1 - 5 nm. Cubic size ⁇ 6 nm.
• Fig. 12C high resolution image. It shows the lattice fringes of cubic NP with inter- fringe spacing of 0.192 nm, close to the lattice spacing of the (200) planes at 0.1908 nm in fee FePt. The inter-fringe distance of spherical NPs are 0.227 nm & 0.192 nm close to fee FePt (110) lattice planes at 0.2202 nm & (200) lattice planes at 0.1908 nm.
• FFT Fast Fourier Transformation
• Cubic formation mechanism could be related to higher concentration of ligand as the complexes are being consumed to form nanoparticles and new ones are being introduced drop-wise.
• XRD patterns are shown in Fig. 13. XRD was carried out over 2 ⁇ ranger over 25 to
• Fig. 13A shows 3 main peaks corresponding FePt (111 ), (200), (220) peaks.
• FePt nanoparticles were synthesised using Na 2 Fe(CO) 4 /Pt(acac) 2 /[P66614][NTf 2 ] according to the the General procedure described above, but in which, after heating up to 150 0 C for 1 h, the reaction mixture was further heated up to 340 0 C for 1 h before cooling to ambient temperature.
• FePt nanoparticles were synthesised using Fe(CO) 5 /Pt(acac) 2 /[P66614][NTf 2 ] and Na 2 Fe(CO) 4 /Pt(acac) 2 /[HMI][NTf 2 ] as described above.
• the order parameter (also refered to as the chemical ordering parameter) displayed in Table 4 below were extracted, as described in the literature, from the ratio of experimental intensity (110) and (111 ) XRD peaks and the values reported for the bulk and was based upon the PDF library card 03-065-9121.
• the temperature of the solution is further increased up to 340 0 C with a heating rate of 15 °C/min.
• the reaction is stopped, and the solution cooled down to room temperature. Nanoparticles are then precipitated by ethanol addition and centrifugation. The supernatant is discarded, while the sediment is dispersed in hexane, and precipitated one more time with ethanol and centrifugation.

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